1. Field of the Invention
The present invention relates, in general, to fluid compressing apparatus. In particular, the invention relates to a scroll type fluid compressing apparatus, which constitutes an element of the refrigerating circuit of an air conditioning apparatus to compress gaseous refrigerant, for example.
2. Description of the Related Art
As is well known, there are several types of a fluid compressor for compressing gaseous refrigerant flowing through a refrigerating circuit of an air conditioning apparatus. One may be a scroll type fluid compressor. The scroll type fluid compressor carries out a compressing operation without using suction and discharge valves. Thus, the scroll type fluid compressor has a low operational noise and a good compressing ability, as compared with a well known rotary type fluid compressor, for example.
A conventional scroll type fluid compressor typically includes a stationary scroll member and a movable scroll member. Each scroll member has a spiral wrap of involute or the like configuration extending from the surface of the end plate thereof. The stationary scroll member and the movable scroll member are arranged to oppose to one another such that the extended end of each spiral wrap is in contact with the surface of the opposing scroll member. As the movable scroll member moves, the volume of a crescent shaped compressing space defined by the pair of spiral wraps is reduced to carry out the compressing operation for a gaseous fluid, e.g., refrigerant, sealed in the compressing space.
In the above-described scroll type fluid compressor, the movable scroll member is mechanically connected to the eccentric portion of an rotational shaft which is driven by a drive unit, and an eccentric rotational movement of the eccentric portion caused by the rotation of the rotational shaft is transmitted to the movable scroll member. Thus, the movable scroll member is apt to orbitally move with a rotation.
An Oldham coupling is used to ensure the orbital movement of the movable scroll member without the rotation. The Oldham ring is arranged between the movable scroll member and a bearing frame fixed in the casing. The compressing unit including the stationary and movably scroll member and the drive unit including a motor are mounted on the bearing frame, respectively. Thus, the bearing frame rotatably supports the rotational shaft, and fixedly supports the stationary scroll member. The Oldham ring includes a ring-shaped base. A pair of keys is oppositely provided to one of the surfaces of the ring-shaped base in one direction. In addition, a pair of keys is oppositely arranged at the other surface in the direction perpendicular to the one direction. A pair of key seats is provided to a surface of the end plate of the movable scroll member facing to the one of the surfaces of the ring-shaped base, and a pair of key seats is further provided to a surface of the bearing frame facing to the other surface of the ring-shaped base. The Oldham ring is mounted on the bearing frame so that the pair of keys provided on the other surface of the ring-shaped base thereof is located in the pair of key seats of the bearing frame. Furthermore, the movable scroll member is mounted on the Oldham ring so that the pair of keys formed on the one of the surfaces of ring-shaped base is located in the pair of key seats of the movable scroll member. The Oldham coupling is assembled, as described above. Since the bearing frame is fixed in the casing, the rotation of the movable scroll member is avoided.
On the other hand, a thrust pressure is generated when the gaseous fluid is pressurized within the movable and stationary scroll members, and is applied to the movable scroll member. If the movable scroll member is directly supported by the bearing frame, the movable scroll member is pressed to the bearing frame by the thrust pressure, and thus a smooth orbital movement of the movable scroll member is not achieved.
To ensure the smooth orbital movement of the movable scroll member, a ring-shaped thrust plate is interposed between the movable scroll member and the bearing frame to support the movable scroll member therethrough. The ring-shaped thrust plate has a smooth surface and a desirable stiffness, and a frictional coefficient thereof is extremely low. The thrust plate is typically made of a cast iron whose surface is treated with a phosphate.
As described above, the Oldham ring and the thrust plate are interposed between the end plate of the movable scroll member and the upper surface of the bearing frame.
Conventional arrangements of the Oldham ring and the thrust plate are shown in FIGS. 1(a) and 1(b). In FIG. 1(a), the inner diameter of Oldham ring 11a is greater than the outer diameter of thrust plate 11b, and thus thrust plate 11b is located inside the Oldham ring 11a. As shown in FIG. 1(b), a relationship between diameters of the Oldham ring 13a and thrust plate 13b is opposite to that shown in FIG. 1(a). Thus, Oldham ring 13a is located inside thrust plate 13b. Two pairs of keys 15a and 15b are provided on the surface of respective Oldham rings 11a and 13a, and a plurality of oil paths 17 are formed in respective thrust plates 11b and 13b in a radial direction.
The above-described arrangements achieve the above described functions of a certain extent. However, in one arrangement shown in FIG. 1(a), since thrust plate 11b supports the movable scroll member with a small ring-shaped area, an amount of the fluctuating movement of the movable scroll member in a thrust direction is increased and the leakage of the gaseous fluid from the compressing space may occur. In another arrangement shown in FIG. 1(b), since the thrust pressure applied to Oldham ring 13a through the movable scroll member is relatively large, a smooth orbital movement of the movable scroll member may not be achieved.
Japanese Laid-open patent 2-39629 published Sep. 6, 1990 discloses another arrangement of an Oldham coupling and a thrust plate wherein an overhang is integrally formed at one side of the thrust plate facing to the bearing surface side of the movable scroll member. The overhang of the thrust plate extends along the surface of the movable scroll member in a radius direction and overhangs above the Oldham ring. The bearing surface of the overhang portion of the thrust plate is formed so that it is elastically deformed to enhance a lubricating ability. Wear or damages of the thrust plate is avoided. However, since the overhang portion of the thrust plate is elastically deformed during the operation, it is difficult to avoid the fluctuating movement of the movable scroll member in a thrust direction, and thus the leakage of the gaseous fluid from the compressing space may occur.